1. Field of the Invention
The present invention relates to a radio communication apparatus and a radio communication method in which transmission and reception are simultaneously performed using two different carrier frequencies.
2. Related Background Art
In an FDD (Frequency Division Duplex) system in conventional radio communications, transmission and reception are performed simultaneously by using an RF (Radio Frequency) carrier frequency which is different for the uplink (mobile station transmission/base station reception) and the downlink (base station transmission/mobile station reception). In an FDD system, a duplexer is used in cases where transmission and reception are performed by using the same antenna. In cases where a duplexer is operating ideally, all the power of the transmission signal is supplied to the antenna and the signal is transmitted by the antenna. In other words, in the case of a base station, a signal is transmitted by the antenna by using the downlink RF carrier frequency and, in the case of a mobile station, a signal is transmitted by the antenna by using an uplink RF carrier frequency. At the same time, all the power of the signal received by the antenna is supplied to the receiver as a received signal. In other words, in the case of the base station, the signal received by the antenna at the uplink RF carrier frequency is supplied to the receiver and, in the case of the mobile station, the signal received by the antenna is supplied to the receiver at the downlink RF carrier frequency.
However, because an actual antenna cannot be made to operate ideally, there is the possibility that a leak of the power in which a portion of the power of the transmission signal is supplied to the receiver will occur. In other words, in the case of the base station, there is the possibility that a portion of the signal transmitted by the base station using the downlink RF carrier frequency will leak to the receiver of the base station. Further, in the case of the mobile station, there is the possibility that a portion of the signal transmitted by the mobile station using the uplink RF carrier frequency will leak to the receiver of the mobile station.
The interference signal that arises as a result of the leak (called a ‘coupling loop interference signal’ hereinbelow) is supplied by being superposed on the desired received signal and leaked to the receiver. The possibility therefore exists that the signal quality of the desired received signal will fall. As a radio communication apparatus that reduces the effect of the coupling loop interference signal that arises as a result of the leak, a radio communication apparatus (booster) with a coupling loop interference signal removal function can be utilized. ‘Suzuki, Ebine, “Configuration and characteristics of a booster for a radio pager system”, IEICE General Conference 1996, B-428, pp. 428, March 1996’ and ‘H. Suzuki, K. Itoh, Y. Ebine, M. Sato, “A booster configuration with adaptive reduction of transmitter-receiver antenna coupling for pager systems”, Proc. of 50th IEEE Vehicular Technology Conference, VTC 1999-Fall, vol. 3, pp. 1516-1520, September 1999’ mention a booster for radio pager system that simultaneously performs interference removal in the RF band in the analog domain and interference removal in the baseband in the digital domain.
Further, the radio communication apparatus which performs transmission and reception simultaneously by using two different carrier frequencies requires adequate separation between RF carrier frequency of the transmission signal and RF carrier frequency of the received signal, in order to reduce the effect of the coupling loop interference signal.
In the case of a radio communication system that uses the FDD system, two frequencies, namely the downlink RF carrier frequency and the uplink RF carrier frequency must be secured. However, in order to alleviate the effect of the coupling loop interference signal that arises in the duplexer as mentioned earlier, the uplink RF carrier frequency and downlink RF carrier frequency must be adequately separated.
However, the radio communication apparatus of the above conventional technology was subject to the problem shown below. That is, in the case of the conventional radio communication apparatus of the FDD system, the uplink RF carrier frequency and the downlink RF carrier frequency must be adequately separated and this amounts to a constraint in the allocation of frequencies to the radio communication system that employs the radio communication apparatus. The securing of the uplink RF carrier frequency and the downlink RF carrier frequency which are adequately separated is a major problem in the effective adoption of the current stringent frequency resources.